System of control



other main switchingra range by field control may be of the familar Patented Aug. 28, 1928.

UNITED STATES IBED I. PARIS, OF MUBBAYBVILLE, AND GEORGE E. SHAW, OI WILKINSIBURG, PENNSYLVANIA, ASSIGNORS 'ZllO WESTINGHOUSE ELECTRIC AND MANUFACTUR- HG COMPANY, A. CORPORATION OF PENNSYLVANIA.

SYSTEM OF CONTROL.

Application filed September Our invention relates to systems of control and it has particular relation to such systems as are employed in connection with rolling mills and the like.

One object of our invention is to provide an improved and simplified system for effecting dynamic braking of a direct-current motor.

Another object of our invention is to prevent an excessive rise in armature voltage durin dynamic braking and drifting peri s.

Other objects of our invention will become apparent from the following description of the operation of the system and from the ap- 15 pended claims. V

In accordance with our invention, a single resistor is employs: for both the starting and the dynamic-bra g operations of the motor, and dynamic braking is efiected without parat-us except the usual single-pole in ependently-operable magnetic reversing-switches. The accelerating switches, together with current-limit accelerating relays, are em loyed to obtain graduated dynamic braking, as well as to accelerate the motor."

- Motors of the type herein employed are commonly adapted for speed control by 'means of a shunt-field rheostat. The speed two-to-one ratio or of a higher ratio. We

preferably employ. a motor-operated field rheostat with suitable means for controlling the operation of the rheostat motor, as hereinafter more fully described.

Our invention will be best understood by reference to the accompanying drawing, in which Fig. 1 is a diagrammatic representation of main circuits and apparatus embodyin our invention,

ig. 2 is a diagrammatic view ofcontrol circuits employed in connection with the system of Fig. 1, and

Fig. 3 is a sequence chart indicating the operation of the main switches.

With reference to the accompanying drawing, a main motor 1 having an armature 2 and a series field-magnet winding 3 is adapted to be connected through a resistor 4 to line conductors 5 and 6. The motor is also provided with a shunt field-magnet winding 7 which is controlled by means of a motor-operated field rheostat 8. In accordance with a familiar practice, the rheostat motor 9, com

as, 1925. serial No. 58,807.

a plurality of field-magnet windin s 10 and 11 that mav be selectively energize for forward or reverse operation. These field windlngs are energized by'means of slow and fast ush-buttons or switches 12 and 13, respect1vely, and the pilot motor circuit is finally interrupted by means of limit switches 14-and15 that are mechanically o erated in accordance with the movement 0 the rheostat arm 16 in the weak field and full field positions, respectively, of the rheostat.

A plurality of accelerating switches 21, 22, 23 and 24 are rovided for controlling the resistor 4 and t ese switches are preferably controlled by means of current limit relays 25, 26,27, 28 and 29 of well-known character. Forward and reverse push-buttons. 31 and 32 are provided for energizing a pair of relays 33 and 34 that respectively control the operati coils 37, 38, 39 and 40 of the forward an reverse switches 41,42, 43 and 44.

In order to prevent plugging the main motor 1, we have employed a pair of relays -45 and 46 each having two operating co1ls 47 and 48 and- 49 and 50, respectively. These relays function in such manner that when the motor is operating in a forward direction, the forward relay 45 occupiesits illustrated closed circuit position and the relay 46 be comes energized to deenergize relay 34, for reverse operation, until the counter E. M. F of the main motor armature has been reduced to a safe value. The coils 47 and 48 of the forward relay 45 are differentially wound so that this relay is inoperative during forward operation: that is, it maintains its closed position. The reverse relay coils 49 and 50 are wound cumulatively with respect to forward 4 0 operation. Since one coil of each of these relays is connected across the motor armature itwill be evident that, when the armature connections. are reversed and the motor is operating in e reverse direction, the compounding effect of these coils is exactly the reverse of that described for forward operation. In other words, the reverse relay 46 remains closed and the forward relay 4'5 0 ens. Any suitable means may be emp oyed, however, to prevent plugging thef motor, which 0 e'ration in certain c asse service is hlg y undesirable and is known to cause undue stressesin the motor and mechanicalparts of the driven apparatus. A

stop button 51 and a no-voltage-relay 52 are provided in the control circuit in a customary manner.

Dynamic braking of the motor is effected by means of a brake ash-button 53 (Fig. 1) which energizes a r ay 54 to maintain the forward switch 43 closed and to efiect the closure of the reversing switch 42 while the other two reversing switches are inoperative.

During dynamic braking, the field. rheostat 8 is returned toward'the full field position and, in order to prevent a too sudden strengthening of the motor field, we have provided a voltage relay 55 having an opersting coil 56 connected across the terminals of t e motor armature 2. If the armature voltage exceeds a predetermined value, relay 55 momentarily interrupts a circuit throug the pilot motor 9, and this relay operation so may be repeated during dynamic braking in accordance with voltage conditions; or until normal voltage obtains. In the. accompan- 'ng drawing, we have designatedthe electrical interlocks, in accordanee with a familiar practice, as being mechanically connected to, and actuated by, the respective switches. Interlocks marked In are closed when the corresponding switches are in or closed and similarly are out when the switches are open.

Assuming-the apparatus in its illustrated and inoperative condition, with no-voltage relay 52 closed, the main motor 1 is started in a familiar manner by means of the forward push-button 31, to energize relay 33, which closes to establish a circuit for the operating coils 37 and 38 of the independentltyl operable reversing switches 41 and 43. e motor accelerates, the starting resistor 4 is gradually shunted by means of the automatlcally controlled accelerating switches 21, 22, 23, and 24, in a familiar manner. The operating coil 49 of reverse relay 46 is of insuflicient strength to operate the relay. The other coil 50 of relay-46 is energized in accordance with the armature voltage and is adapted to assist coil 49 as'the motor operates m-a forward direction. The reversing relay 34, therefore, is now inoperative, as tenously explalned, and the motor cannot reversed by operation of the reversing pushbutton 32 until the brake push-button 53 has first beenactuated to efiect dynamic braking.

energized by a circuit extending from the motor armature 2 through resistor 4,'brake push-button 53, the interlocks 41-out and 44-out side of the motor armature. In order to com plate the dynamic braking circuit, the two reversing switches 41 and 43 must be opened ply operation of the stop button 51 so that epperatmg coil 57 of relay 54 may be ena cult is for the. coils 38 To establish dynamic braking, relay 54 isand the relay coil 57 to the other rgized. Upon the closure of relay 54, a cirbe 1m esa 41a .nd 39 of switches 42 and43, and, upon the closure of these switches, a dynamic braking circuit becomes effective, extending from the motor armature 2- throughresistor 4 and re- It will be noted that,during the dynamic braking period, accelerating switch 24 is operative because interlock 42-out 1s mcluded in the circuit of its actuating coil,

whereas switch 42 is closed at this time.

Referring to Fig. 1 a circuit is established for the pilot motor 9 extending from conductor 5 through relay 55, interlock 24-out, limit switch-14, field winding 10 and the pilot motor armature to conductor 6 whereby the field rheostat8 is actuated toward the full field position. If the main motor load, dur ing braking, is such thatthe armature voltage rises above a predetermined value, relay 55 is actuated to interrupt the pilot motor circuit until a roper voltage obtains, when the operation 0 the pilot motor is continued.

It is sometimes necessary to momentarily operate the main motor to reverse 'the rolls of a steel mill, for example, and this reverse operation may be efiected from standstill, or from-low motor speed, by operating the reverse button. 32 to energlze relay 34, which relay can only be energized when'relay 46 is closed, and when the armature voltage has been reduced to a low value. The motor may then be automatically accelerated, in a manper-similar to that described for forward operation, by means of the acceleratin 'relays and switches, and the motor may t e after be disconnected from the line and d namic braking applied by operation of e Ill! brake push button 53 as hereinbefore de-- scribed.

It should be noted that whereas we have employed the same resistor for both starting and dynamic brakin operations, we have not employed addition main switching apparatus, but, in accordance with our invention, we are enabled to utilize the reversing and acceleratin switches to accomplish the desired result. %n so far as we are aware, this system, as applied to reversing control, is new and its uti ity will be at once Although we have set forth the preferred embodiment of our invention, it wlll be understood that various modifications thereofmay be made without departing. from the s therefore, that only such limitations shall appen ed y irit and scope of the invention. We desire,

thereon as are-indicated in the I responsive means We claim as our invention:

1. The combination with a motor and a resistor therefor, of a pair of independently operable switches for connecting said resistor. 1

operatlon, a pa1r :of-

in circuit for forward independently operable switches for connecting said resistor in circuit for reverse-opera' tion, means for energizing one switch of each of said pairs to establish a dynamic-braking circuit comprising said resistor, and loadfor varying the efl'ecting value of said resistor.

2. The combination with a motor and a resistor therefor, of a pair of independently operable switches for connecting said resistor in circuit for forward operation, a pair of independently operable switches for connecting said resistor in circuit for reverse? operation, means for ener izing one switch of each of said pairs to esta lish a dynamic-braking circuit comprising said resistor, and loadresponsive means for varying the efi'ective value of said resistor during starting and during dynamic braking.

3. The combination with a motor and a. re-

sistor therefor, of a pair of independently operable switches for connecting said-resistor in circuit for forward operation, a pair of independently operable switches for connecting said resistor in circuit for reverse operation, means for energizing one switch of each of said pairs to establish a dynamic-braking circuit comprising said resistor, means for insuring the completion of said dynamic braking circuit prior to establishing said reversing connections and load-responsive means for varying-the effective value of said main motor during the braking period.

In testimony whereot, we have'hereunto subscribed our names this first day of Sep- 40 tember, 1925.

FRED M. PARKS. GEORGE R. SHAW. 

